The present invention has as its subject a bell furnace and hardening vat arrangement, the furnace and the vat being placed at different levels, one of these elements or each of them being movable horizontally relative to one another, the arrangement including means for supporting a charge composed of parts contained in a cage, these means being integral with the bell and projecting from the sidewall and on the inside of the latter, the arrangement further comprising a lift capable of entering the bell.
The problems encountered at the time of the hardening operations in heat treatment installations including the apparatus of the type just of referred to are essentially four in number: first, that of oxidation of the parts when they enter into contact with the oxygen of the air after having been brought to high temperature in the furnace and, if the case arises, of oxidation of the fluid used as a hardening bath, in the second place, in the cases where the vat, situated below the furnace, contains a gas protecting the hardening bath, that of the rapid dispersion of this gas at the time of the manipulation consisting in transferring the charge from the furnace into the bath; in the third place, that, connected moreover with the two problems previously referred to, of air pollution; finally, that of flexibility and correlatively of autonomy, as well as of the space requirement of the installation in general and of the rapidity of execution of the manipulations connected with the various treatment operations. The fact that all the problems must be solved jointly, without the solution provided to one of them hampering that of the others, further increases the difficulty.
The bell furnace/hardening vat arrangements utilized in the known heat treatment installations illustrate this difficulty. Thus, the patent DE 19 42 801, though it supplies a first solution to the problem of flexiblity by providing means permitting the bell furnace to be brought above the vat, leaves the problem of the oxidation of the parts untouched. In the same way, though the bell has means for supporting the charge, the lift raising the latter in the furnace must effect a rotation of 45.degree. to set down or inversely to release the charge from these means. Moreover, the use of a block and tackle remains necessary for certain manipulations. Patent GB No. 899,793, on the other hand, proposes a solution to the problem of oxidation, the furnace and the vat forming a quasi monolithic structure. But the arrangement presents two major drawbacks which are, on the one hand, the totally static and non-versatile characters of the installation and, on the other hand, the bulk thereof, the overall height of the installation exceeding three times the height of a charge, the latter being conveyed laterally, in a passage situated between the furnace and the vat. Finally, the duration of the handling still remains too long in the two cited prior disclosures.
Patents FR-1,521,505 and DE-3,525,635 teach the possibility of a vertical movement of the joined furnace/bell unit with a view to obtaining imperviousness either at the time of the heating operation (French patent) or at the time of the hardening operation (German patent). The devices described present a series of major drawbacks; there shall be retained as such, as concerns FR-1,521,505, the absence of imperviousness, the immersion of the plug, the considerable energy losses, the pollution of the charge and of the air; as concerns DE 3,525,635, the absence of a mooring system, the permanent support of the charge by the lift of the vat, and the total absence of autonomy of the furnace.
The present invention has as an object to provide an arrangement of the kind mentioned at the beginning which contributes, especially with the invention which is the subject of a parallel application of the same applicant, a joint solution to the problems enumerated, and to avoid the drawbacks set forth.
To this end, the arrangement answering the general concept of the preamble of claim 1 is characterized in that means are provided for subjecting solely the bell to a relative vertical movement in relation to the furnace, the furnace remaining fixed, while the vat is under the furnace, so that the mere bottom rim of the bell is brought against the top peripheral portion of the vat, the bell and the vat then forming a tight enclosure.
The arrangement further comprises a lift capable of entering into the bell, the furnace being equipped with means for release of the charge, capable of displacing said support means between an active position where they extend under the perimeter of the charge and a withdrawn position where they release the perimeter of the charge and permit its vertical displacement by means of the lift.